The invention relates to flame retardant polycarbonate resin compositions and articles made therefrom having high transparency.
Polycarbonate resin compositions are used in a variety of fields including automobiles, electric, electronic, machinery, building and construction applications and the like. Resins used for some of the above-mentioned applications must pass strict flame retardancy requirements, e.g., the flame-retardancy standard according to UL-94 in the U.S.A. Such tests typically involve exposing an object made from the resin to a flame or other heat source for a certain time period. The object may fail the test by catching fire, remaining on fire for too long a period, or by partially melting and dripping flaming resin droplets on a flammable material placed below the object. In some applications requiring miniaturization and/or very thin molded articles, there is an increased risk of a flaming droplet arising from the thinned part of the shaped article. Resins used in such applications need to fulfill the requirements for obtaining a V0-rating according UL-94, i.e. short flame-out times (<10 s) and no (burning) drips that ignite a layer of cotton placed beneath the object.
Satisfactory UL94 V0-ratings of polymers do not always guarantee a good fire performance in building and construction applications. One reason for this discrepancy is the duration requirements for the UL94 tests. In fire tests for the building and construction areas, exposure time to an heat source (i.e. open flame or radiant panel) is in the order of minutes (equal to or more than 5 minutes), while UL94-testing requires much shorter exposure times (2 times 10 seconds).
In certain building and construction applications, there are various government-mandated tests, each with its own specifications and requirements, for evaluating the fire resistance of thermoplastics. A European Single Burner Item (SBI) test has been developed to harmonize the different national standards and better measure fire performance of construction products. This test is defined to cover all important parameters of the various country-specific tests, some of which are speed of flame spread, time to ignition, height of flames, smoke production and production of burning droplets. The formation of burning droplets is critical for passing the French test norm NF-P-92-501 and for determining the overall rating (M1-M4) for the material and application. The formation of droplets is measured in French test norm NF-P-92-505 (also known as the “dripping test”) and this test, is considered to be one of the more aggressive tests for fire performance of building and construction materials.
Prior art flame retardant systems for polycarbonate compositions typically employ phosphates and halogens. The phosphates lower the use temperature of the polycarbonate as well as its impact strength. As pointed out by various environmental protection groups, the use of halogens possibly generates toxic fumes when a resin composition burns. Therefore, there is need for an improved flame-retardant resin composition.
Guanidine salts are known to impart flame retardant characteristics to resins used in various applications. JP Patent No. 8603995 discloses the addition of 1-30 wt. % guanidine cyanurate in various resin compositions including polyester, nylon, polycarbonate, epoxy, phenol, and polyurethane. U.S. Pat. No. 4,341,694 discloses compositions displaying intumescent and flame retardant characteristics comprising: a resin selected from polyolefins, polyvinylaromatic resins, polycarbonates, polyacrylates, polyamides, PVC and blends thereof; and about 20-60% by weight of a) a bicyclic phosphate compound, and b) a nitrogen compound selected from the group including guanidine and salts thereof.
Applicants have surprisingly found that guanidine inorganic salts, when added to a polycarbonate resin composition, surprisingly and dramatically increase its pass rate in a specific dripping test, while still retaining its transparent characteristics and other properties.